relibc_pthreads-emb/sem_trywait.c

/*
 * -------------------------------------------------------------
 *
 * Module: sem_trywait.c
 *
 * Purpose:
 *	Semaphores aren't actually part of the PThreads standard.
 *	They are defined by the POSIX Standard:
 *
 *		POSIX 1003.1b-1993	(POSIX.1b)
 *
 * -------------------------------------------------------------
 *
 * --------------------------------------------------------------------------
 *
 *      Pthreads-embedded (PTE) - POSIX Threads Library for embedded systems
 *      Copyright(C) 2008 Jason Schmidlapp
 *
 *      Contact Email: jschmidlapp@users.sourceforge.net
 *
 *
 *      Based upon Pthreads-win32 - POSIX Threads Library for Win32
 *      Copyright(C) 1998 John E. Bossom
 *      Copyright(C) 1999,2005 Pthreads-win32 contributors
 *
 *      Contact Email: rpj@callisto.canberra.edu.au
 *
 *      The original list of contributors to the Pthreads-win32 project
 *      is contained in the file CONTRIBUTORS.ptw32 included with the
 *      source code distribution. The list can also be seen at the
 *      following World Wide Web location:
 *      http://sources.redhat.com/pthreads-win32/contributors.html
 *
 *      This library is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU Lesser General Public
 *      License as published by the Free Software Foundation; either
 *      version 2 of the License, or (at your option) any later version.
 *
 *      This library is distributed in the hope that it will be useful,
 *      but WITHOUT ANY WARRANTY; without even the implied warranty of
 *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *      Lesser General Public License for more details.
 *
 *      You should have received a copy of the GNU Lesser General Public
 *      License along with this library in the file COPYING.LIB;
 *      if not, write to the Free Software Foundation, Inc.,
 *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include "pthread.h"
#include "semaphore.h"
#include "implement.h"


int
sem_trywait (sem_t * sem)
/*
 * ------------------------------------------------------
 * DOCPUBLIC
 *      This function tries to wait on a semaphore.
 *
 * PARAMETERS
 *      sem
 *              pointer to an instance of sem_t
 *
 * DESCRIPTION
 *      This function tries to wait on a semaphore. If the
 *      semaphore value is greater than zero, it decreases
 *      its value by one. If the semaphore value is zero, then
 *      this function returns immediately with the error EAGAIN
 *
 * RESULTS
 *              0               successfully decreased semaphore,
 *              -1              failed, error in errno
 * ERRNO
 *              EAGAIN          the semaphore was already locked,
 *              EINVAL          'sem' is not a valid semaphore,
 *              ENOTSUP         sem_trywait is not supported,
 *              EINTR           the function was interrupted by a signal,
 *              EDEADLK         a deadlock condition was detected.
 *
 * ------------------------------------------------------
 */
{
  int result = 0;
  sem_t s = *sem;

  if (s == NULL)
    {
      result = EINVAL;
    }
  else if ((result = pthread_mutex_lock (&s->lock)) == 0)
    {
      /* See sem_destroy.c
       */
      if (*sem == NULL)
        {
          (void) pthread_mutex_unlock (&s->lock);
          errno = EINVAL;
          return -1;
        }

      if (s->value > 0)
        {
          s->value--;
        }
      else
        {
          result = EAGAIN;
        }

      (void) pthread_mutex_unlock (&s->lock);
    }

  if (result != 0)
    {
      errno = result;
      return -1;
    }

  return 0;

}				/* sem_trywait */